1. Field of the Invention
The present invention relates to a wireless communication system providing wireless communications and a mobile terminal, and particularly, to a method allowing a terminal with data to be transmitted in an uplink direction to transmit a radio resource allocation request message to a base station by effectively using radio resource(s) to its maximum level. More particularly, the present invention relates to a method allowing the terminal to select a radio resource allocation request message of a proper format according to a situation of radio resource(s) or the amount of data of each channel and transmit the same to the base station.
2. Description of the Related Art
FIG. 1 shows a network structure of the E-UMTS, a mobile communication system, applicable to the related art and the present invention. The E-UMTS system has been evolved from a UMTS system, for which the 3GPP is proceeding with the preparation of the basic specifications applicable thereto. The E-UMTS system may be classified as an LTE (Long Term Evolution) system.
The E-UMTS network may be divided into an E-UTRAN and a core network (CN). The E-UTRAN includes a terminal (referred to as ′UE (User Equipment), hereinafter), a base station (referred to as an eNode B, hereinafter), and an access gateway (AG) located at an end of a network and connected with an external network. The AG may be divided into a part handling processing of user traffic and a part processing control traffic. In this case, the AG for processing user traffic and the AG processing control traffic may communicate with each other by using a new interface. One or more cells may exist for a single eNode B. An interface for transmitting the user traffic or the control traffic may be used between eNodes. The CN may include a node for registering an AG and a user of a UE. An interface for discriminating the E-UTRAN and the CN may be used.
Layers of a radio interface protocols between the terminal (UE) and the network can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model widely known in communication systems. A physical layer belonging to the first layer (L1) provides an information transfer service using a physical channel, and an RRC (Radio Resource Control) layer positioned at the third layer serves to control radio resource(s) between the terminal and the network. To this end, the RRC layer exchanges an RRC message between the terminal and the network. The RRC layer may be distributively positioned at network nodes such as the eNode B, the AG, etc., or may be positioned only at the eNode B or at the AG.
FIG. 2 illustrates a radio interface protocol architecture based on a 3GPP radio access network specification between the terminal and the base station. The radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane for transmitting user information and a control plane for transmitting control signals (signaling). The protocol layers can be divided into the first layer (L1), the second layer (L2), and the third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model widely known in communication systems.
The radio protocol control plane in FIG. 2 and each layer of the radio protocol user plane in FIG. 3 will now be described.
The physical layer, namely, the first layer (L1), provides an information transfer service to an upper layer by using a physical channel. The physical layer is connected to an upper layer called a medium access control (MAC) layer via a transport channel, and data is transferred between the MAC layer and the physical layer via the transport channel. Meanwhile, between different physical layers, namely, between a physical layer of a transmitting side and that of a receiving side, data is transferred via the physical channel.
The MAC layer of the second layer provides a service to a radio link control (RLC) layer, its upper layer, via a logical channel. The RLC layer of the second layer may support reliable data transmissions. The function of the RLC layer may be implemented as a function block in the MAC. In this case, the RLC layer may not exist. A PDCP layer of the second layer performs a header compression function for reducing the size of a header of an IP packet including sizable unnecessary control information, whereby an IP packet such as IPv4 or IPv6 can be effectively transmitted in a radio interface with a relatively small bandwidth.
A radio resource control (RRC) layer located at the lowest portion of the third layer is defined only in the control plane, and handles the controlling of logical channels, transport channels and physical channels in relation to configuration, reconfiguration and release of radio bearers (RBs). The radio bearer refers to a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN.
A downlink transport channel transmitting data from the network to the terminal includes a BCH (Broadcast Channel) that transmits system information and a downlink SCH (Shared Channel) that transmits user traffic or a control message. Traffic or a control message of a downlink multicast or broadcast service may be transmitted via the downlink SCH or a downlink MCH (Multicast Channel). An uplink transport channel transmitting from the terminal to the network may include an RACH (Random Access Channel) that transmits an initial control message and an uplink SCH that transmits user traffic or a control message. A general method for receiving data by the terminal in the LTE system will now be described.
The base station and the terminal mostly transmit and receive data via a physical channel PDSCH (Physical Downlink Shared Channel0 using a transport channel DL-SCH, except for a particular control signal or particular service data. Information about a terminal (one or more terminals) to which data of the PDSCH is to be transmitted, information about how the terminals receive the PDSCH data, information about how the PDSCH data is to be received or decoded, or the like are included in a PDCCH (Physical Downlink Control Channel) and transmitted.
For example, it is assumed that a particular PDCCH including information regarding data, which is CRC-masked with an RNTI (Radio Network Temporary Identity (or Identifier)) of ‘A’ and transmitted via transmission format information (e.g., a transmission block size, a modulation and coding information, etc.) of ‘C’ via radio resource (e.g., a frequency position) of ‘B’, is transmitted in a particular sub-frame. Then, one or two or more terminals located in a corresponding cell monitor the PDCCH by using RNTI information of their own, and if they have the ‘A RNTI’ at a corresponding point of time, the terminals would receive the PDCCH and also receives the PDSCH indicated by ‘B’ and ‘C’ via the information of the PDCCH.
In this process, the RNTI is transmitted in order to information about to which terminals allocation information of radio resource(s) transmitted via each PDCCH is pertinent. The RNTI includes a dedicated RNTI and a common RNTI. The dedicated RNTI is used to transmit/receive data to/from a particular terminal, and used by the terminal when information of the terminal is registered in the base station. Meanwhile, the common RNTI is used to transmit or receive data to or from terminals that have not been allocated a dedicated RNTI because their information was not registered to the base station, or transmit information, such as system information, commonly used by a plurality of terminals. For example, an RA-RNTI or a T-C-RNTI in the RACH process is the common RNTI.
As mentioned above, the base station and the terminal(s) are two main entities that constituting the E-UTRAN. Radio resource(s) include uplink radio resource and downlink radio resource in a cell. The base station handles allocation and controlling of the uplink radio resource and the downlink resource in the cell. Namely, the base station determines which terminal uses which radio resource(s) in a certain moment. For example, the base station may determine that frequency 100 MHz to 101 MHz is allocated to a user No. 1 to transmit downlink data for 0.2 seconds after 3.2 seconds. After such determination, the base station may inform the corresponding terminal accordingly to allow the terminal to receive downlink data. Also, the base station determines when and which terminal would transmit data in an uplink direction by using which and how much radio resource(s), and allows a corresponding terminal to transmit data during the corresponding time. Such dynamic management of radio resource(s) by the base station is effective, compared with the related art in which a single terminal keeps using a single radio resource while a call is in connection. This is irrational in the aspect that, recently, many services are based on IP packets. That is, most packet services do not constantly generate packets during a call-connected time but there are many sections during which nothing is transmitted, and in this sense, constantly allocating radio resource(s) to a single terminal would be ineffective. Thus, the E-UTRAN system employs the method of allocating radio resource(s) to the terminal only when the terminal requires them or only while there is service data.
In the LTE system, in order to effectively use radio resource(s), the base station should know which data each user waits for. In case of data to downlink, the downlink data is transferred from the access gateway. Namely, the base station knows how much data should be transmitted to each user via the downlink. Meanwhile, in case of data to uplink, if each terminal does not inform the base station about data it intends to directly transmit to uplink, the base station could not know how much uplink radio resource(s) each terminal requires. Thus, for a proper uplink radio resource allocation, each terminal should provide information required for scheduling of radio resource(s) to the base station.
Namely, if a terminal has data to be transmitted, it informs the base station about that, and the base station then transmits a radio resource allocation message to the terminal based on the information.
In this case, when the terminal informs the base station that it has data to be transmitted, actually, the terminal informs the base station about the amount of data gathered in its buffer. It is called a buffer status report (BSR).
As stated above, if a terminal has data in its buffer and certain conditions are met, the terminal is to transmit a BSR to the base station.
In this respect, however, the BSR has no direct connection with user data, which the terminal and the base station actually want to exchange. Namely, the BSR is used to merely transfer information required for effectively allocating radio resource(s) to the terminal by the base station, rather than transferring actual user data.
Thus, it is better to have the smaller the BSR, thereby reducing a waste of radio resource(s) used for transmitting the BSR. Namely, the BSR is preferred to be as simple as possible.
There are several logical channels for a single terminal, and each logical channel has a different priority level. For example, in case of an SRB (Signaling Radio Bearer) used for exchanging an RRC message by the base station and the terminal, if there is data in the SRB, the terminal should inform the base station accordingly as soon as possible, and in this case, the base station should allocate radio resource(s) to the terminal more preferentially. Meanwhile, if there is data in a logical channel for a VoIP (Voice over Internet Protocol) and if there are other terminals than the terminal, the terminals having channels set with a priority level higher than the VoIP, and there is data in the channels with the higher priority level in the cell, the terminal would not need to quickly transmit the BSR to the base station and the base station also would not need to immediately allocate radio resource(s) to the terminal. Thus, the BSR would be better to be as accurate as possible in consideration of a difference of each channel. Namely, in this case, as the BSR becomes large, it can include more detailed information, which promotes an improvement of performance at the side of a scheduler of the base station.
Thus, a method for effectively informing the base station about a buffer status of the terminal while satisfying the two conflicting conditions is required.